A camera flying through a fractal. Instead of filling a fixed volume once and looking at it, the grid is rebuilt every frame around wherever the camera currently is, so you are always sampling the part of infinite fractal space you happen to be in.
Three things make that work. The camera follows a smooth curve that passes exactly through its waypoints and has no corners at the joins.
Then there is the collision problem, and it is a real one: a Mandelbulb has no corridors, and a straight line through one hits a wall almost immediately.
The solution is that the fractal already tells you how far the nearest surface is, because the renderer needs that number to march its rays. The camera reads the same number, sees how close it has come, and steers away along the direction in which that distance grows fastest.